JP5161737B2 - smoke detector - Google Patents

Description

  The present invention relates to a smoke detector that detects and reports smoke generated during a fire.

  Conventionally, as this kind of smoke detector A, there is a detection space in the housing 20 as shown in FIG. 12, and an LED (light emitting section) 7 that intermittently outputs light toward the detection space, and an LED 7 There is known a device including a photodiode (light receiving unit) PD that is disposed at a position where direct light from the light is not incident and converts received light into a current (see, for example, Patent Document 1). In this smoke detector A, when smoke flows into the detection space, the light from the LED 7 is diffusely reflected by the smoke in the detection space, so that the amount of light received from the LED 7 at the photodiode PD increases, The amount of current output from the diode PD increases.

  The LED 7 and the photodiode PD constitute an optical block 23 together with a light projecting lens 21 disposed in front of the LED 7 and a light receiving lens 22 disposed in front of the photodiode PD. The housing 20 has an opening on the lower surface and a body 24 housing the optical block 23 so that light from the LED 7 is emitted toward the opening, and a bottomed cylindrical shape with an upper surface opening. And a cover 25 coupled to the body 24 so as to cover the opening. An opening window for taking in smoke is formed in the peripheral wall of the cover 25, and the detection space is formed in the cover 25. Here, in the cover 25, an insect net 26 for preventing insects from entering the detection space and a labyrinth 27 for preventing external light from entering the detection space are arranged so as to surround the detection space. The labyrinth 27 employs a complicated structure having a complicated optical path in order to prevent incidence of various disturbance light from a fluorescent lamp, an incandescent lamp, and the like.

  In this type of smoke detector A, as shown in FIG. 13, a current-voltage conversion circuit (IV) that converts the input current from the photodiode PD into a voltage and outputs it to the detection circuit 1 housed in the housing 20. Conversion circuit) 4 is provided. Further, the output voltage of the current-voltage conversion circuit 4 is set as an output signal through the amplifier circuit 6 ′ and the filter circuit 5 ′, and the output signal is input to the alert determination circuit 10 ′. When the fire judgment level is reached, the alarm circuit (buzzer or the like) 28 is configured to issue an alarm. The detection circuit 1 is provided with an LED drive circuit 29 that periodically emits light from the LED 7, a power supply circuit 30 that supplies power to each circuit, and an interlocking circuit 31 that links other reporting means and the like. .

  Accordingly, when the smoke detector A is intermittently driven as shown in FIG. 14A and pulsed light is output from the LED 7 as shown in FIG. 14B, smoke flows into the detection space. When the photodiode PD receives light from the LED 7, as shown by a solid line in FIG. 14C, the instantaneous value of the output signal Vout greatly fluctuates from the reference operating point and reaches the fire determination level in the figure. Become. On the other hand, if there is no smoke in the detection space, the instantaneous value of the output signal Vout does not reach the fire determination level as shown by the broken line in FIG.

  By the way, disturbance light from fluorescent lamps, incandescent lamps, and the like usually has a smaller fluctuation amount with time than pulsed light from the LED 7, so that when this type of disturbance light enters the photodiode PD, The diode PD outputs a current with small temporal fluctuation (hereinafter referred to as “disturbance light component”), and the operating point of the output signal Vout may fluctuate. If the operating point of the output signal Vout itself fluctuates due to the influence of disturbance light components, the output signal Vout does not reach the fire determination level even though the photodiode PD receives light from the LED 7 There is a possibility that the output signal Vout reaches the fire determination level and becomes a non-fire report even though the photodiode PD does not receive the light from the LED 7.

However, in the smoke detector A, the labyrinth 27 prevents various disturbance lights from a fluorescent lamp, an incandescent lamp, and the like from entering the detection space. Therefore, the operating point of the output signal Vout due to the influence of the disturbance light is prevented. Fluctuations are suppressed, and the above-mentioned misreports and non-fire reports are unlikely to occur.
Japanese Patent No. 2783945 (page 1-2)

  In the above-described smoke detector A, the structure of the labyrinth 27 for preventing disturbance light from entering the detection space is complicated, and the cost for manufacturing the labyrinth 27 hinders the cost reduction of the entire smoke detector A. Therefore, it is desired to reduce the cost of the smoke detector A by simplifying the structure of the labyrinth 27 as much as possible or omitting the labyrinth 27 itself. However, if the labyrinth 27 is simplified or omitted, the amount of disturbance light received by the photodiode PD increases, the disturbance light component included in the input current Iin increases, and the operating point of the output signal Vout fluctuates. There is a problem that it is easy to generate information and non-fire reports.

  The present invention has been made in view of the above-described reasons, and an object thereof is to provide a smoke detector that is less prone to missing or non-fire reports while simplifying or omitting the labyrinth.

  According to the first aspect of the present invention, a light emitting unit that intermittently outputs pulsed light toward the detection space, and a light emitting unit that is diffusely reflected by smoke that does not enter the direct light from the light emitting unit and flows into the detection space A light receiving unit that receives light and converts it into current, a sensor output processing unit that converts an input current input from the light receiving unit into an output signal composed of a voltage signal, and the output An arithmetic processing unit that determines the presence or absence of smoke in the detection space based on the signal, and the sensor output processing unit transiently changes the instantaneous value of the output signal according to the fluctuation amount when the input current fluctuates, The arithmetic processing unit detects the instantaneous value of the output signal as a measured value at each of the first and second sampling timings set in the transient response period of the output signal with respect to the input current, and detects by the detection unit Both A determination means for determining the presence or absence of smoke in the detection space by comparing a difference value between the measured values with a predetermined threshold value, and the first and second sampling timings calculate a difference between the two measured values. It is set so that it may occur.

  According to this configuration, the arithmetic processing unit detects the instantaneous value of the output signal as the measured value at the first and second sampling timings set in the transient response period of the output signal with respect to the input current, and both measured values. Since the presence or absence of smoke in the detection space is determined by comparing the difference value between them with a predetermined threshold value, the disturbance light component included in the input current increases and the operating point of the output signal may fluctuate. Even if it exists, the said disturbance light component hardly affects the said difference value, Therefore, the presence or absence of the smoke in a detection space can be determined without being influenced by the disturbance light component. As a result, the labyrinth is simplified or omitted, and there is an advantage that it is difficult to generate misreports and non-fire reports.

  According to a second aspect of the present invention, in the first aspect of the invention, the sensor output processing unit includes bandpass means for generating a gain peak in a frequency band determined according to a pulse width of light from the light emitting unit. The output signal is output as a signal that swings from the operating point, which is an instantaneous value in a state where the light receiving unit is not receiving light from the light emitting unit, to both sides of the positive and negative sides, and the detection means is provided on both sides of the operating point. Each of the measurement values is detected.

  According to this configuration, since the detection means detects the measurement values on both sides of the operating point of the output signal, the difference value between the two measurement values is increased as compared with the case where both measurement values are detected on one side of the operating point. There is an advantage that the SN ratio can be improved.

  According to a third aspect of the present invention, in the second aspect of the invention, the bandpass means includes an integrating circuit that integrates the input current and a differentiating circuit that differentiates the output of the integrating circuit.

  According to this configuration, the output signal can be a signal that swings from the operating point to both the positive and negative sides with a relatively simple configuration using the integration circuit and the differentiation circuit.

  According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the pulse width of the light from the light emitting unit and the first and second sampling timings are determined based on the same clock. It is characterized by that.

  According to this configuration, even if the pulse width of the light from the light emitting unit varies due to the temperature characteristics of the drive circuit of the light emitting unit, the first and second sampling timings also change as the pulse width varies. Therefore, it is possible to suppress variations in measurement values due to variations in the pulse width of light from the light emitting unit.

  According to a fifth aspect of the present invention, in any of the second to fourth aspects of the present invention, the first and second sampling timings are set before the peak of the instantaneous value of the output signal. And

  According to this configuration, even if the gain of the sensor output processing unit varies due to the temperature characteristics of the sensor output processing unit, the gain is higher than when the measured value is detected at the peak of the instantaneous value of the output signal. Variations in measured values due to variations can be reduced.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the arithmetic processing unit uses the instantaneous value of the output signal as a preliminary value during a preliminary period before the light emitting unit outputs light. If the preliminary value is not within a predetermined normal range, the determination by the determination means is not performed.

  According to this configuration, in the state where the operating point itself of the output signal fluctuates due to the influence of the disturbance light component and is out of the normal range, the determination by the determination means is not performed. Therefore, the output signal is influenced by the influence of the disturbance light component. It is possible to prevent misreporting due to the fact that the fluctuation amount of the output signal due to saturation and the light receiving unit receiving light from the light emitting unit cannot be accurately detected.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, the sensor output processing unit is intermittently driven, and the light emitting unit outputs light while the sensor output processing unit is being driven. It is characterized by.

  According to this configuration, the average power consumption can be kept lower than when the sensor output processing unit is always driven. Even if the instantaneous value of the output signal may fluctuate when the sensor output processing unit is activated, the detection space is not affected by the fluctuation of the output signal when the sensor output processing unit is activated. The presence or absence of smoke inside can be determined.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the detection means comprises an AD converter that quantizes the instantaneous value and obtains the measured value including a digital value. And

  According to this configuration, since the detection means includes the AD converter, the circuit configuration of the arithmetic processing unit can be relatively simplified.

  In the present invention, the arithmetic processing unit detects the instantaneous value of the output signal as a measured value at the first and second sampling timings set in the transient response period of the output signal with respect to the input current, and Since the presence / absence of smoke in the detection space is determined by comparing the difference value with a predetermined threshold value, there is an advantage that misreporting and non-fire reporting are unlikely to occur while simplifying or omitting the labyrinth.

(Embodiment 1)
The smoke detector A of the present embodiment has a detection space in the housing 20 as in the conventional configuration shown in FIG. 12, and a light emitting unit that intermittently outputs pulsed light toward the detection space; A light receiving unit that is disposed at a position where direct light from the light emitting unit is not incident and converts received light into current, and a detection circuit 1 that detects smoke in the detection space based on an input current from the light receiving unit. . In the smoke detector A, when smoke flows into the detection space, the amount of light received from the light emitting unit at the light receiving unit increases due to diffuse reflection of the light from the light emitting unit with the smoke in the detection space, The amount of current output from the light receiving unit increases. The smoke detector A exemplified here uses a battery as a power source, and is intermittently driven in order to reduce the average power consumption and extend the life of the battery.

  As shown in FIG. 1, the detection circuit 1 of the present embodiment converts the input current Iin input from the light receiving unit into an output signal Vout whose voltage value varies according to the variation of the input current Iin and outputs the output signal Vout. An output processing unit 2 and an arithmetic processing unit 3 provided at a subsequent stage of the sensor output processing unit 2 and determining the presence or absence of smoke in the detection space based on the output signal Vout are provided.

  As shown in FIG. 1, the sensor output processing unit 2 converts the input current Iin input from the input terminal Tin into an output voltage whose voltage value varies according to the variation of the input current Iin, and outputs the converted output voltage. A circuit 4; a high-pass filter 5 connected to the output of the current-voltage conversion circuit 4; and a voltage amplification circuit 6 that amplifies the output voltage that has passed through the high-pass filter 5.

  The current-voltage conversion circuit 4 has a configuration in which a conversion resistor R1 is connected between an inverting input terminal and an output terminal of an operational amplifier OP1 serving as an input terminal Tin, and a reference voltage Vs1 is applied to a non-inverting input terminal of the operational amplifier OP1. Have A photodiode PD (see FIG. 12) as a light receiving unit is connected to the input terminal Tin of the current-voltage conversion circuit 4, and an input current Iin is input from the photodiode PD.

  Here, the current-voltage conversion circuit 4 of this embodiment has a capacitor C1 connected in parallel to the conversion resistor R1 and also functions as a low-pass filter, and passes an input current Iin having a predetermined cutoff frequency fc0 or less. The circuit constants of the conversion resistor R1 and the capacitor C1 are set. This cut-off frequency fc0 is expressed by fc0 = 1 / (2π × r1 × c1) using the resistance value r1 of the conversion resistor R1 and the constant c1 of the capacitor C1, and at least the photodiode PD is an LED 7 (light emitting portion). It is set so as to pass a pulsed input current Iin generated when light from (see FIG. 12) is received.

  Further, since the current-voltage conversion circuit 4 also functions as an integration circuit with the above-described configuration, the output voltage of the current-voltage conversion circuit 4 changes with the passage of time from the change point of the input current Iin so that the input voltage Iin changes with a predetermined time delay. Thus, the voltage value is changed.

  The high-pass filter 5 is composed of a series circuit of a capacitor C2 and a resistor R2 connected to the output terminal of the operational amplifier OP1, and an end portion (one end portion of the resistor R2) opposite to the operational amplifier OP1 in the series circuit. A reference voltage Vs2 is applied. The output of the high pass filter 5 is output from the connection point between the capacitor C2 and the resistor R2. The cut-off frequency fc1 of the high-pass filter 5 is expressed by fc1 = 1 / (2π × r2 × c2) using the resistance value r2 of the conversion resistor R2 and the constant c2 of the capacitor C2, and at least the photodiode PD is from the LED 7 It is set to pass a pulsed output voltage generated when light is received.

  In the voltage amplifier circuit 6, the non-inverting input terminal of the operational amplifier OP2 is connected to the output end of the high pass filter 5 (the connection point between the capacitor C2 and the resistor R2), and the inverting input terminal of the operational amplifier OP2 is connected to the inverting input terminal via the resistor R3. A reference voltage Vs2 is applied, and a parallel circuit of a resistor R3 and a capacitor C3 is connected between the inverting input terminal and the output terminal. The voltage amplified by the voltage amplification circuit 6 is output as an output signal Vout to the arithmetic processing unit 3 at the subsequent stage.

  With the above configuration, the sensor output processing unit 2 outputs, based on the operating point according to the fluctuation of the input current Iin, with the instantaneous value of the output signal Vout when the input current Iin from the photodiode PD is zero as the operating point. The signal Vout is changed. At this time, the instantaneous value of the output signal Vout fluctuates transiently according to the fluctuation amount of the input current Iin.

  The arithmetic processing unit 3 digitally outputs a sample hold circuit (S / H circuit) 8 that holds an instantaneous value of the output signal Vout input from the sensor output processing unit 2 and an output signal Vout input from the sensor output processing unit 2. It has an AD converter 9 as a detection means for converting into a value, and a determination circuit 10 as a determination means for determining the presence or absence of smoke in the detection space based on the output (digital value) of the AD converter 9.

  The AD converter 9 samples (samples) the output signal Vout and quantizes it, thereby detecting the instantaneous value of the output signal Vout at the sampling timing as a digital value. Here, sampling is performed twice each time the LED 7 emits light once, and thereby, it becomes possible to extract a fluctuation component of the output signal Vout caused by the photodiode PD receiving light from the LED 7.

  That is, the AD converter 9 performs the first sampling at the first sampling timing set immediately after the LED 7 emits light, and the instantaneous value of the output signal Vout at this time is quantized as the first measurement value. To do. Then, at the second sampling timing set after a predetermined time from the first sampling timing, the sample hold circuit 8 holds the instantaneous value of the output signal Vout, and in this state, the second sampling is performed, The instantaneous value of the output signal Vout at the sampling timing is quantized as a second measurement value.

  Here, since the instantaneous value of the output signal Vout changes with a predetermined time delay when the photodiode PD receives the pulsed light from the LED 7, at least the change of the instantaneous value is at least in the first and second sampling timings. The transient response period of the output signal Vout with respect to the input current Iin is set so as to be reflected between the first measurement value and the second measurement value.

  Therefore, when the LED 7 emits pulses as shown in FIG. 2A, and smoke exceeding a predetermined amount flows into the detection space, the output signal Vout is as shown in FIG. 2B. Since there is a relatively large variation from the first sampling timing to the second sampling timing, a relatively large difference occurs between the first measurement value AD1 and the second measurement value AD2 obtained by the AD conversion unit 9. It will be. On the other hand, if smoke exceeding a predetermined amount does not flow into the detection space, the output signal Vout does not vary greatly from the first sampling timing to the second sampling timing as shown in FIG. A difference as large as that shown in FIG. 2B does not occur between the first measurement value AD1 and the second measurement value AD2 obtained by the AD conversion unit 9.

  The determination circuit 10 includes a storage unit (not shown) that stores first and second measurement values obtained by the AD converter 9, and a first measurement value and a second measurement stored in the storage unit. A calculation unit (not shown) for determining the presence or absence of smoke in the detection space by obtaining a difference from the value and comparing the difference value with a predetermined threshold (hereinafter referred to as a fire determination level). ing. In the calculation unit, smoke exists when the difference between the first and second measurement values AD1 and AD2 is equal to or higher than the fire determination level as shown in FIG. If the difference between the first and second measured values AD1 and AD2 is smaller than the fire determination level as shown in FIG. 2C, no smoke is present (the smoke concentration that can be determined as a fire has not been reached). judge.

  The determination result in the determination circuit 10 is sent to the alarm circuit 28 (see FIG. 13), and is notified by an appropriate method when a fire occurs (that is, when it is determined that there is smoke). The smoke detector A may be configured to send the determination result to an external device such as a home information board.

  According to the configuration described above, the presence / absence of smoke is determined based on the difference between the instantaneous value of the output signal Vout at the first sampling timing and the instantaneous value of the output signal Vout at the second sampling timing. Even if various disturbance lights from fluorescent lamps, incandescent lamps, etc. enter the detection space, and the operating point of the output signal Vout may fluctuate due to the influence of the disturbance light, it is difficult to generate misreports and non-fire reports. There are advantages. That is, in this embodiment, since the presence / absence of smoke is determined based on the amount of change in the output signal Vout when the LED 7 emits pulses, the fire is caused even though the photodiode PD receives light from the LED 7. It is possible to avoid a misreport without being determined to occur, or a non-fire report due to a determination that a fire has occurred even though the photodiode PD does not receive light from the LED 7.

  For example, when light from a fluorescent lamp that is lit with a commercial power supply (60 Hz AC power supply) using a copper-iron ballast is incident on the detection space, as shown in FIG. The light fluctuates in a sinusoidal manner at a frequency of 120 Hz. At this time, since the fluctuation cycle of the output signal Vout is 8.33 ms, assuming that the amplitude of the output signal Vout is “2” in peak to peak, the influence of the fluorescent lamp during 120 μs. The maximum fluctuation amount of the output signal Vout that can be generated is “0.09035” from 360 ° × (120 μs / 8.3 ms) = 5.184 ° and sin (5.184 °) = 0.09035. Since this value (0.09035) is about 4.5% of the original amplitude (2) (0.09035 / 2 = 0.045175), the first and second sampling timings are set at intervals of 120 μs. For example, the fluctuation amount of the output signal Vout caused by the influence of the fluorescent lamp can be attenuated (−26.9 dB) to about 4.5%.

  Therefore, when the structure of the labyrinth is simplified as much as possible, or the labyrinth itself is omitted to reduce the cost of the smoke detector A, the amount of disturbance light received by the photodiode PD increases, and the input current Iin is increased. Even if the disturbance light component included becomes large and the operating point of the output signal Vout fluctuates, it is difficult to generate a false alarm or a non-fire alarm.

  In addition, since the detection circuit 1 is assumed to be intermittently driven in the present embodiment, the output signal Vout may fluctuate relatively large immediately after the sensor output processing unit 2 is started as shown in FIG. As described above, the presence or absence of smoke is determined based on the amount of change in the output signal Vout when the LED 7 emits pulses. It is possible to avoid generating non-fire reports.

  As shown in FIG. 5, when the disturbance light component included in the input current Iin exceeds a certain level due to the influence of disturbance light, the output signal Vout may be saturated. In particular, when the battery is used as the power source of the smoke detector as in this embodiment, the output signal Vout is relatively easily saturated because the power supply voltage of the operational amplifier is low and the dynamic range of the operational amplifier is relatively narrow. If the output signal Vout saturates in the middle when the input current Iin increases, the output signal Vout cannot follow the fluctuation of the input current Iin. Therefore, the photodiode PD receives the light from the LED 7 and receives a pulse-like shape. Even if the input current Iin occurs, there is a possibility that the amount of change in the output signal Vout does not reach the fire determination level and may be reported as unreported (in FIG. ).

  Therefore, in the present embodiment, as shown in FIG. 5B, the instantaneous value of the output signal Vout is read as the preliminary value AD0 during the preliminary period before the LED 7 emits light, and the preliminary value AD0 is determined in a normal range. The arithmetic processing unit 3 includes preliminary determination means (not shown) that prevents the determination by the determination circuit 10 if it is not within. That is, the preliminary determination means detects the amount of change from the operating point of the output signal Vout due to the influence of ambient light as the preliminary value AD0 before the output signal Vout fluctuates due to the pulse emission of the LED 7, and the amount of change is detected. If it exceeds the normal range, it is determined that the output signal Vout is likely to be saturated, and the determination circuit 10 is not allowed to determine whether smoke is present. As a result, the output signal Vout is saturated due to the influence of disturbance light, and it is possible to eliminate false alarms due to the fact that the fluctuation amount of the output signal Vout caused by the pulse emission of the LED 7 cannot be accurately detected.

(Embodiment 2)
As shown in FIG. 6, the smoke detector A of the present embodiment generates a voltage corresponding to the magnitude of the low frequency component below the predetermined first cut-off frequency fc1 among the output voltage output from the current-voltage conversion circuit 4. The sensor output processing unit 2 includes a first feedback circuit 11 for output, and a shunt resistor R5 inserted between the output of the first feedback circuit 11 and the input terminal Tin of the current-voltage conversion circuit 4. . Further, in the present embodiment, the second feedback circuit 12 that outputs a voltage corresponding to the magnitude of the low frequency component below the predetermined second cutoff frequency fc2 among the output voltage of the current-voltage conversion circuit 4, and the second The sensor output processing unit 2 is provided with a shunting transistor Q1 that draws a current corresponding to the magnitude of the output of the feedback circuit 12 from the input current Iin.

  The first feedback circuit 11 integrates the inverting amplifier circuit 13 that inverts and amplifies the output voltage of the current-voltage conversion circuit 4 and the output voltage that is inverted and amplified by the inverting amplifier circuit 13 and corresponds to an integral value component of the output voltage. And a first integration circuit 14 that outputs a voltage.

  The first integrating circuit 14 connects the inverting input terminal of the operational amplifier OP3 to the output of the inverting amplifier circuit 13 via the resistor R6, and connects the capacitor C4 between the inverting input terminal and the output terminal of the operational amplifier OP3. Configured as a low-pass filter having a time constant determined by the resistor R6 and the capacitor C4. The integration circuit 14 has a time constant set so as to have a first cut-off frequency fc1 that blocks an output voltage corresponding to an input current Iin generated when at least the photodiode PD receives light from the LED 7.

  The inverting amplifier circuit 13 is for making the output of the integration circuit 14 in phase with the output voltage of the current-voltage conversion circuit 4, and is connected to the output terminal of the current-voltage conversion circuit 4 via the resistor R7. Are connected, and a resistor R8 is connected between the inverting input terminal and the output terminal of the operational amplifier OP4. Note that the non-inverting input terminals of the operational amplifiers OP3 and OP4 are set to the same potential as the reference voltage Vs1 with respect to the circuit ground.

  Thus, when the input current Iin includes a pulse component and a disturbance light component generated when the photodiode PD receives the pulsed light from the LED 7, the integrated voltage output from the first integrating circuit 14 is The voltage corresponds to the disturbance light component. At this time, the phase of the input current Iin is once inverted by the current-voltage conversion circuit 4, and the phase is also inverted once by the inverting amplification circuit 13 and the integration circuit 14, respectively. An integrated voltage having a phase opposite to that of Iin appears. Here, since the input terminal Tin of the current-voltage conversion circuit 4 is at the same potential as the reference voltage Vs1 with respect to the circuit ground, a potential difference obtained by subtracting the integrated voltage from the reference voltage Vs between both ends of the shunt resistor R5. Will occur. That is, the current corresponding to the magnitude of the integrated voltage can be drawn from the input current Iin by flowing the current to the shunt resistor R5. Therefore, when the disturbance light component is included in the input current Iin, the disturbance light component Is subtracted from the input current Iin to be removed from the output voltage.

  By the way, in the detection circuit 1 of the present embodiment, the second feedback circuit 12 samples and holds the output of the second integration circuit 15 that integrates the output voltage of the current-voltage conversion circuit 4 and the output of the second integration circuit 15. And a sample hold circuit 16 for performing the above operation.

  The second integration circuit 15 connects the inverting input terminal of the operational amplifier OP5 to the output terminal Tout of the current-voltage conversion circuit 4 via the resistor R9, and a capacitor is connected between the inverting input terminal and the output terminal of the operational amplifier OP5. C5 is connected, and functions as a low-pass filter having a time constant determined by the resistor R9 and the capacitor C5. The time constant is set so that the second integration circuit 15 has a second cutoff frequency fc2 (that is, fc1 <fc2) higher than the first cutoff frequency fc1 of the first integration circuit 14 described above. The non-inverting input terminal of the operational amplifier OP5 is set to the same potential as the reference voltage Vs1 with respect to the circuit ground.

  The shunting transistor Q1 is inserted between the input terminal Tin of the current-voltage conversion circuit 4 and the circuit ground, and allows a current corresponding to the output of the second integrating circuit 15 to flow from the input terminal Tin to the circuit ground. Here, it is composed of an N-channel MOSFET. The shunting transistor Q1 has a drain connected to the input terminal Tin of the current-voltage conversion circuit 4 and a source connected to the circuit ground, and a gate connected to the output (operational amplifier) of the second integrating circuit 15 via the sample hold circuit 16. The output terminal is connected to the output terminal of OP5.

  The sample hold circuit 16 includes a normally closed first switch SW1 inserted between the output of the second integrating circuit 15 and the gate of the shunting transistor Q1, and between the gate of the shunting transistor Q1 and the circuit ground. And by turning off the first switch SW1 at a predetermined timing, the output of the integrating circuit 15 at the predetermined timing is maintained as the output voltage of the capacitor C6.

  With the above-described configuration, the second integration circuit 15 integrates the output voltage of the current-voltage conversion circuit 4, so that a low frequency component having a frequency equal to or lower than the second cutoff frequency fc2 of the output voltage is Will appear in the output. At this time, the phase of the input current Iin is once inverted by the current-voltage conversion circuit 4 and further the phase is also inverted by the second integration circuit 15, so that the output of the integration circuit 15 has a low frequency in phase with the input current Iin. Ingredients appear. Here, since the output of the integrating circuit 15 is applied to the gate of the shunting transistor Q1 via the sample and hold circuit 16, when the switch SW1 of the sample and hold circuit 16 is on, the drain-source region of the shunting transistor Q1 is turned on. In this case, a current corresponding to the output level of the integrating circuit 15 flows. Therefore, a low frequency component equal to or lower than the second cut-off frequency fc2 included in the input current Iin can be extracted to the shunting transistor Q1, and the gain of the low frequency component can be lowered as the entire sensor output processing unit 2.

  Here, when the switch SW1 of the sample hold circuit 16 is turned off, the output of the integration circuit 15 and the gate of the shunting transistor Q1 are cut off, but the output of the integration circuit 15 is maintained as the voltage across the capacitor C6. Therefore, a current corresponding to the output level of the integrating circuit 15 immediately before the switch SW1 is turned off can continue to flow between the drain and source of the shunting transistor Q1. In other words, when the sample-and-hold circuit 16 is activated by turning off the switch SW1 of the sample-and-hold circuit 16, the upper limit value of the frequency of the current that can flow between the drain and source of the shunting transistor Q1 (second cutoff frequency fc2). However, the DC component can be removed from the output voltage by continuously pulling it out to the shunting transistor Q1.

  In the present embodiment, the timing at which the switch SW1 of the sample and hold circuit 16 is turned off is a period during which the smoke detector LED 7 outputs pulsed light and detects the presence or absence of smoke flowing into the detection space (hereinafter referred to as a sensing period). It is set according to). That is, the sensor output processing unit 2 of the present embodiment converts the pulsed input current Iin generated when the photodiode PD receives light from the LED 7 during the sensing period into a voltage signal and outputs it as an output signal Vout. Therefore, the switch SW1 is turned off during the sensing period so that the input current Iin during the sensing period is not drawn out by the shunting transistor Q1.

  More specifically, the second cutoff frequency fc2 of the second integration circuit 15 is set closer to the frequency of the pulsed input current Iin than the first cutoff frequency fc1 of the first integration circuit 14. Therefore, when the switch SW1 is on, the input current Iin is drawn to the shunting transistor Q1, and the gain of the input current Iin may be reduced as a whole of the sensor output processing unit 2. Therefore, in this embodiment, the switch SW1 is turned off during the sensing period to operate the sample and hold circuit 16, thereby avoiding the input current Iin being drawn to the shunting transistor Q1, and the sensor output processing unit 2 as a whole. A high gain of the input current Iin is secured.

  Therefore, during the sensing period in which the switch SW1 is turned off, the output of the second feedback circuit 12 is fixed to a value immediately before the switch SW1 is turned off, so that there is no fluctuation in the DC component included in the input current Iin. Although it can be continuously extracted to the shunting transistor Q1, with regard to the low frequency component with fluctuation included in the input current Iin, even if the low frequency component is a low frequency component equal to or lower than the second cutoff frequency fc2, It cannot be pulled out to the shunting transistor Q1. However, even during the sensing period, the low frequency component below the first cut-off frequency fc1 can be extracted to the shunt resistor R5 by taking it out as the output of the first feedback circuit 11.

  According to the detection circuit 1 having the configuration described above, by using the shunt resistor R5 and the shunt transistor Q1 as means for extracting the low frequency component of the input current Iin, the low frequency component is extracted only by the shunt resistor R5. Compared to the case, a larger current component can be extracted.

  In the example of FIG. 6, a second switch SW2 connected in parallel to the conversion resistor R1 of the current-voltage conversion circuit 4 is provided. The switch SW2 is a normally closed switch that is turned off at the same timing as the first switch SW1, and has a function described below.

  That is, if only the first switch SW1 is provided, the cutoff frequency fc2 of the second feedback circuit 12 is shifted to the high frequency side when the first switch SW1 is turned on. As for the frequency characteristics of the gain of the entire circuit 2, the gain on the low frequency side is crushed when the first switch SW1 is turned on, and the cutoff frequency fc0 of the current-voltage conversion circuit 4 and the second cutoff of the second feedback circuit 12 A gain peak occurs between the frequency fc2 and the system easily oscillates. In other words, since the output signal Vout is in a state of being easily oscillated, there is a problem that if the first switch SW1 is turned off when the output signal Vout is low, the rise of the output signal Vout is delayed.

  In contrast, in the present embodiment in which the second switch SW2 connected in parallel with the conversion resistor R1 is provided, the first switch SW1 is turned on by turning on the second switch SW2 together with the first switch SW1. While the switch is on, both ends of the conversion resistor R1 are connected to crush the gain of the sensor output processing unit 2, and the above-described gain peak can be eliminated. As a result, it is possible to suppress the oscillation of the system due to the first switch SW1 being turned on.

  By the way, in the present embodiment, the frequency characteristics of the gain in the sensor output processing unit 2 are set to a predetermined frequency (here, 2 kHz) as a reference frequency as shown in FIG. By crushing the gain on the frequency side, a gain peak is generated at the reference frequency. That is, in the first embodiment, as shown in FIG. 7B, the gain frequency of the sensor output processing unit 2 has a flat gain over a relatively wide frequency band (here, 0.1 Hz to 8 kHz). In contrast to the characteristic being set, in the present embodiment, a gain is given to a relatively narrow frequency band centered on the reference frequency.

  Specifically, the time constant of the high-pass filter 5 is adjusted to cause the high-pass filter 5 to function as a differentiating circuit, and the signal integrated by the integration circuit (resistor R1 and capacitor C1) provided in the current-voltage conversion circuit 4 is obtained. Differentiation is performed by the high-pass filter 5 at the subsequent stage. In short, the band-pass means in which the low-pass filter function of the current-voltage conversion circuit 4 as the integration circuit and the high-pass filter 5 as the differentiation circuit cause a gain peak in a predetermined frequency band (frequency band centered on the reference frequency). Function as.

  Here, the above-mentioned reference frequency is determined according to the pulse width when the LED 7 emits pulses so that the amplitude of the output signal Vout becomes maximum with respect to the input current Iin. For example, when the pulse width of pulse emission is 90 μs, the reference number wave number is desirably 2 kHz. Thus, by giving a gain to a narrow frequency band centered on the reference frequency determined according to the pulse width of the input current Iin, the amplitude of the output signal Vout can be increased with respect to the input current Iin.

  Therefore, in the configuration of the first embodiment, when the photodiode PD receives light from the LED 7 and the pulsed input current Iin flows as shown in FIG. 8A, the output signal Vout is as shown in FIG. As shown, it starts to decrease from the operating point with the rise of the input current Iin, and starts to rise toward the operating point with the falling of the input current Iin. In this way, the output signal swings only to one side of the operating point (here, the side where the voltage is reduced).

  In contrast, in this embodiment, when the photodiode PD receives light from the LED 7 and a pulsed input current Iin flows as shown in FIG. 9A, the output signal Vout is as shown in FIG. As shown, it starts to decrease from the operating point with the rise of the input current Iin, starts to increase with the falling of the input current Iin, and then reaches the peak beyond the operating point and then decreases toward the operating point. Begin to. That is, the pulse signal integrated by the integration circuit of the current-voltage conversion circuit 4 is differentiated by the high-pass filter 5 at the subsequent stage, and becomes an output signal Vout that swings on both sides of the operating point. Thus, the output signal Vout swings on both sides of the operating point.

  Therefore, in the present embodiment, for example, by sampling each of the upper and lower peaks in the output signal Vout, the difference (ΔV) between both the first and second measured values is made larger than in the configuration of the first embodiment. There is an advantage that the SN ratio is improved. In short, when the output signal Vout swings only to one side of the operating point as in the first embodiment, the difference between the first and second measured values can only be taken as the difference from the operating point of the output signal Vout. However, when the output signal Vout fluctuates on both sides of the operating point as in this embodiment, the magnitude between the first and second measured values is about twice as large from the operating point to one peak. Differences can be taken. As a result, the signal component extracted from the output signal Vout increases, and the SN ratio is improved.

  As specific configurations, conversion resistor R1 = 5 MΩ, capacitor C1 = 14 pF, resistor R2 = 2 MΩ, capacitor C2 = 50 pF, resistor R3 = 39 kΩ, resistor R4 = 740 kΩ, capacitor C3 = 30 pF, shunt resistor R5 = If 400 kΩ, resistor R6 = 500 kΩ, capacitor C4 = 200 pF, resistor R7 = 500 kΩ, resistor R8 = 40 kΩ, resistor R9 = 250 kΩ, capacitor C5 = 30 pF, capacitor C6 = 60 pF, as shown in FIG. A gain peak having a reference frequency of 2 kHz occurs.

  Further, the configuration of the present embodiment has an advantage that the sample hold circuit 8 in the arithmetic processing unit 3 is not required because it is not necessary to perform sample hold in order to detect the second measurement value as in the first embodiment. .

  Incidentally, each of the first and second sampling timings is set near the peak (lower limit value and upper limit value) of the output signal Vout from the viewpoint of increasing the difference between the first and second measurement values. It is desirable. However, since the magnitude of the peak of the output signal Vout depends on the frequency characteristics of the gain of the sensor output processing unit 2, the gain of the sensor output processing unit 2 depends on the temperature characteristics of the components of the sensor output processing unit 2. When the frequency characteristic changes, the peak of the output signal Vout may change accordingly. Naturally, if the peak of the output signal Vout changes, the magnitude of the difference between the first and second measured values also changes, so in this embodiment, due to variations in the frequency characteristics of the gain of the sensor output processing unit 2. In order to minimize the variation in the difference between the first and second measured values, the first and second sampling timings are set before the peak of the output signal Vout in the time axis direction, respectively.

  That is, as shown in FIG. 10, by setting the first and second sampling timings before the peak of the output signal Vout when the frequency characteristic of the gain of the sensor output processing unit 2 is in a steady state, Compared with the case where the first and second sampling timings are set at the peak of the output signal Vout in the state, the variation in the measured value due to the gain variation in the sensor output processing unit 2 can be suppressed to a small value. The shift amount from the peak of the output signal Vout in the steady state at each of the first and second sampling timings is determined so that the variation of each measurement value falls within the specified target accuracy. In the illustrated example, the pulse width for causing the LED 7 to emit light is set to 90 μs, and the time point of 80 μs and the time point of 200 μs from the light emission start time are set as the first and second sampling timings, respectively.

  The pulse width of the input current Iin is as shown in FIG. 11A (in the figure, the steady state is “typ”, the maximum value is “max”, and the minimum value is “min”). 29 (see FIG. 13) may vary within a certain range due to temperature characteristics. When the pulse width of the input current Iin changes, the peak position of the output signal Vout in the time axis direction also changes as shown by the two-dot chain line in FIG. 11B, so the sampling timing is fixedly set. As a result, the first and second measurement values vary. Therefore, in this embodiment, the clock in the LED drive circuit 29 that defines the pulse width of the input current Iin is shared with the clock for determining the sampling timing.

  Thus, even if the pulse width of the input current Iin changes due to the temperature characteristics of the LED drive circuit 29, the sampling timing is determined in accordance with the changed pulse width, so the pulse width of the input current Iin It is possible to suppress variations in the first and second measurement values due to variations in.

  In the present embodiment, the description has been made on the assumption that the input current Iin flows into the input terminal Tin of the current-voltage conversion circuit 4 when the photodiode PD receives light. However, the input current Iin with respect to the input terminal Tin It may be assumed that the direction is reversed and the input current Iin flows out from the input terminal Tin when the photodiode PD receives light. In this case, the shunting resistor R5 and the shunting transistor Q1 do not function to draw the input current Iin from the input terminal Tin but function to add the input current Iin to the input terminal Tin. Specifically, the shunting transistor Q1 is composed of a P-channel MOSFET connected between the input terminal Tin and the reference power supply, and a current corresponding to the output of the second integrating circuit 15 is supplied from the reference power supply to the input terminal Tin. Configured to flow through.

  Other configurations and functions are the same as those of the first embodiment.

It is a schematic circuit diagram which shows the detection circuit of Embodiment 1 of this invention. It is a time chart which shows operation | movement same as the above. It is a wave form diagram which shows operation | movement same as the above. It is a time chart which shows operation | movement same as the above. It is a time chart which shows operation | movement same as the above. It is a schematic circuit diagram which shows the detection circuit of Embodiment 2 of this invention. (A) is a characteristic diagram showing the gain of the sensor output processing unit of the above, (b) is a characteristic diagram showing the gain of the sensor output processing unit of the first embodiment. 3 is a time chart illustrating the operation of the detection circuit according to the first embodiment. 6 is a time chart illustrating the operation of the detection circuit according to the second embodiment. It is a time chart which shows operation | movement same as the above. It is a time chart which shows operation | movement same as the above. It is a schematic block diagram which shows the conventional smoke detector. It is a schematic block which shows a structure same as the above. It is a timing chart which shows operation | movement same as the above.

Explanation of symbols

2 Sensor output processing unit 3 Arithmetic processing unit 7 LED (light emitting unit)
9 AD converter (detection means)
10. Determination circuit (determination means)
A Smoke detector Iin Input current PD Photodiode (receiver)
Vout output signal

Claims (8)

  A light emitting unit that intermittently outputs pulsed light toward the detection space, and a position where light from the light emitting unit diffusely reflected by smoke flowing into the detection space does not enter the direct light from the light emitting unit A light receiving unit that receives light and converts it into a current, a sensor output processing unit that converts an input current input from the light receiving unit into an output signal composed of a voltage signal, and a detection space based on the output signal The sensor output processing unit transiently changes the instantaneous value of the output signal according to the amount of fluctuation when the input current fluctuates, and the calculation processing unit Detecting means for detecting the instantaneous value of the output signal as a measured value at each of the first and second sampling timings set in the transient response period of the output signal for the output signal, and between the two measured values detected by the detecting means The difference value And determining means for determining the presence or absence of smoke in the detection space by comparing with a threshold value of the first and second sampling timings are set so as to cause a difference between the two measured values Smoke detector characterized by.   The sensor output processing unit includes bandpass means for generating a gain peak in a frequency band determined according to a pulse width of light from the light emitting unit, and the light receiving unit outputs the output signal from the light emitting unit. 2. The signal output as an oscillating signal from an operating point, which is an instantaneous value when light is not received, to both positive and negative sides, and the detection unit detects the measured values on both sides of the operating point, respectively. The smoke detector according to 1.   3. The smoke detector according to claim 2, wherein the bandpass means includes an integrating circuit for integrating the input current and a differentiating circuit for differentiating the output of the integrating circuit.   The smoke detector according to claim 2 or 3, wherein the pulse width of the light from the light emitting unit and the first and second sampling timings are determined based on the same clock. .   5. The smoke detector according to claim 2, wherein the first and second sampling timings are respectively set before a peak of an instantaneous value of the output signal.   The arithmetic processing unit reads an instantaneous value of the output signal as a preliminary value during a preliminary period before the light emitting unit outputs light, and if the preliminary value is not within a predetermined normal range, the determination unit The smoke detector according to any one of claims 1 to 5, wherein the determination is not performed.   The smoke detection according to any one of claims 1 to 6, wherein the sensor output processing unit is driven intermittently, and the light emitting unit outputs light while the sensor output processing unit is being driven. vessel. The smoke detector according to any one of claims 1 to 7, wherein the detection unit includes an AD converter that quantizes the instantaneous value to obtain the measurement value including a digital value.

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